1. Field of the Invention
The present invention relates to a low noise video preamplifier, and in particular to a low noise video preamplifier having very wide dynamic range and suitable for use with laser guided weapon systems.
2. Description of the Prior Art
Laser-guided weapon systems generally utilize multiple laser detectors which typically detect very short pulses of laser energy at a relatively low repetition rate. The intensity of the received energy and, consequently, the peak value of each pulse may vary widely over the trajectory of the weapon. Movement of the target, changes in reflectivity, variations in the propagation path, presence of smoke and other obstructions in the optical path, and similar factors can produce rapid and large variations in signals from the detector. To obtain reliable control signals for operation of the guidance system, it is necessary to maintain amplitude proportionality among the received pulses. Therefore, stringent requirements are placed on the automatic gain control circuits of such a system to prevent overloading, clipping, and other nonlinearities in the signal circuits.
An additional requirement is for circuits that can be produced in LSI form for use with small ordnance devices such as cannon launched projectiles. Generally, a preamplifier may be utilized which is driven by the laser detector and which has its gain controllable by means of an automatic gain control (AGC) voltage produced by the signal processing circuits. The preamplifier requires a very wide bandwidth to be able to pass the narrow pulses and is required to have a very low noise figure. A typical dynamic range to be achieved is on the order of 120 dB. Although gain controlled preamplifiers are well known in the prior art, none having the requisite wide dynamic range, low noise characteristic, and wide bandwidth which could be implemented in monolithic form was known.